Correlated electron systems possess complex electronic phase diagrams that are exceptionally sensitive to the orbital occupancy of electrons and chemical/carrier doping. In particular, electronic phase transitions observed in RNiO3 perovskite nickelates (where R stands for rare earth lanthanide elements) are of broad interest in materials physics to understand band structure and oxide electronics such as but not limited to electronic switches.
In general, defects in oxide semiconductors make possible novel functionalities of great interest in resistance switching, superconducting, electrochromic and sensing devices. Correlated oxides are extremely sensitive to such defects, due to their sharp and nonlinear response on the shifting of strongly polarizable metal-oxygen bonds and strong correlations between valence electrons. The electronic properties of correlated oxides are exceptionally sensitive to chemical disorder.
Perovskite nickelates are correlated oxides with sharp thermally-driven insulator-metal transition. Among nickelates, SmNiO3 (samarium perovskite nickelate, also referred to in this application as SNO) is the first rare earth nickelate with insulator-metal transition temperature TIM (˜400 K) above room temperature, and is of great interest for the integration of correlated oxides with conventional circuits.
Conductance modulation in nickelates such as SmNiO3(SNO) is usually within one-two orders of magnitude across the transition boundary, which may originate from the subtle charge disproportionation. During the thermally driven phase transition in SNO, the NiO6 octahedron buckles at below metal-insulator transition (MIT) temperature, which reduces the orbital overlapping and renders an insulating phase. Charge disproportionation has been proposed as the cause for SNO's insulating phase during thermally driven phase transitions in SNO.
Practically, however, resistance modulation in SNO as a cause of the thermally driven insulator-metal transition is usually limited to within only one-two orders (from room temperature to 200° C.). Also, the extremely short electrostatic screening length makes the resistance modulation challenging via electrostatic gating even with ionic liquids.